This project focuses on individual differences in physical and affective functioning in newborns and the long-term consequences of such differences. One study is concerned with the ways certain psychophysiological and behavioral signs of arousal or irritability (e.g., heart rate, heart rate variability, vagal tone, colic, sleeplessness, crying) in the first months of life are related to measures of the child's temperament, emotional expressiveness, and physiology at later ages. Preliminary analyses of the data from the initial (5 and 7 month) phases of the study revealed that there was significant temporal stability for the vagal tone, heart rate, and maternal ratings of temperament. Additionally, when compared to infants with moderate vagal tones, 5-month-old infants who had extremely high vagal tone were rated as more fussy and those who had extremely low vagal tone were rated as more unadaptable. At 7 months, the infants with the lowest vagal tone were rated as more unadaptable than the infants with either moderate or with the highest vagal tone scores. In a second project concerned with interactions between lower-class Hispanic mothers and their infants, SSED staff are studying the effects of maternal behavior, maternal characteristics, family patterns, and infant characteristics upon the subsequent socioemotional development of these Hispanic children. Observing these Hispanic individuals in their homes facilitates the development of culturally-sensitive criteria for evaluating normative social behavior and the development of parent-infant relationships.